Since required capacity and allocated radio resources are constant for respective connections, conventional circuit switched communication networks such as CDMA (Code Division Multiple Access) or GSM (Global System for Mobile) have only to detect the number of subscribers in order to perform load balancing. Hereinafter, one connection is referred to as a service flow (SF).
FIG. 1 is a flow diagram illustrating a conventional connection admission control (CAC) flow for a new service flow generation request. If an already allowed QoS (Quality of Service) service flow is to change QoS requirements, the CAC flow may be performed from step 104 omitting steps 100 and 102.
Referring to FIG. 1, in step 100, a base station receives a call connection request from a user terminal.
In step 102, the base station compares the already allowed service flow number NCID with the maximum available service flow number NMAX—CID. If the NMAX—CID is smaller than or equal to the NCID, the flow proceeds to step 110. The base station rejects the call connection request in step 110. If the NMAX—CID is greater than the NCID, the flow proceeds to step 104. In step 104, the base station checks whether the call is a QoS call. If a QoS call, the flow proceeds to a corresponding mode. If not a QoS call, the flow proceeds to step 106. In step 106, the base station sets a BE (Best Effort) service. In step 108, the base station accepts the call connection request. According to embodiments, step 102 may be subdivided into detailed steps as follows. First, the number of service flows allowable by the base station or the subcell is checked, and if allowed, the number of service flows allowable for a corresponding user terminal is detected with respect to each of uplink and downlink or the total sum of the downlink and the uplink are detected.
However, in the third-generation wireless networks such as WiMAX or 3GPP2, a single base station must simultaneously support multimedia applications having various traffic characteristics (e.g., real time vs. non real time, and constant bit rate (CBR) vs. variable bit rate (VBR)) and high-grade access techniques (e.g., AMC, HARQ, PF scheduling, and MIMO) are differentially applied depending on the traffic characteristics, thus making it difficult to perform load balancing by checking only the subscriber number and the connection number. Due to such various traffic characteristics, for connection admission control, the bandwidth requirement capacity for each connection must be checked for each traffic type, and the process requirement time for each connection must be differentially scheduled by a scheduler.
In relation to load balancing in a broadband communication system, the current IEEE 802.16 standards are as follows.
First, according to the IEEE 802.16 standard, if a serving FA (frequency assignment) cannot support a corresponding user terminal in an initial network entry, network reentry, quick connection step (QCS) and handover after a ranging request (RNG-REQ), a corresponding FA is aborted and another FA (four (4) bytes, in units of KHz) is overridden to report the same to a corresponding user terminal through a ranging response (RNG-RSP).
Second, a base station notifies a subcell identifier BSID in the case of BSHO-REQ (BS HO REQuest), MSHO-REQ (MS HO REQuest), BSHO-RSP (BS HO ReSPonse), SCN-REQ (SCaNning interval allocation REQuest), or SCN-RSP (SCaNning interval allocation ReSPonse), and notifies an FA in the case of RNG-RSP. The BSID and the subcell are mapped in one-to-one correspondence (1 subcell=1FA/1sector). Thus, if multiple FAs are used for one sector, as many BSIDs as the FAs are used for one sector. On the contrary, if three sectors are allocated to one FA, three BSIDs are used for a corresponding FA.
Third, through the RNG-RSP (BSHO-REQ and BSHO-RSP), the CAC results are provided by service level prediction (SLP). That is, the SLP value specifies a service level that can be expected by a user terminal from a base station. For example, if the SLP is 0, it means that no service is possible for a user terminal. If the SLP is 1, it means that some service is available for one or several service flows authorized for a user terminal. If the SLP is 2, it means that for each authorized service flow, a MAC connection can be established with QoS specified by the AuthorizedQoSParamSet. If the SLP is 3, it means that no service level prediction is available.
However, the current IEEE 802.16 standard has the following problems in relation to load balancing.
First, the standard fails to specify how to make a load check by a base station in a ranging request, how to select an FA to be overridden in a ranging response if a serving subcell cannot support a corresponding user terminal, how to process an overridden FA by a user terminal in a ranging response, and how to perform a communication process between the system and the user terminal after the ranging response, failing to provide a complete load balancing scheme. For example, a user terminal may first perform an initial network entry process for an FA not selected by a base station based on the radio environment estimated by the user terminal itself. In this case, because the base station selects another FA by load balancing, this process may be repeated. As another example, a FA is notified in overriding but a user terminal is uncertain of which subcell it is to select, because one FA may have multiple subcells.
Second, downlink radio conditions of FAs in the same sector are similar but that of FAs in different sectors may be greatly different. In this case, if a base station considers only load balancing without considering radio conditions, because a user terminal will attempt a handover to the side with good radio conditions, the base station and the user terminal are different in requirements, which may cause a ping-pong phenomenon.
Third, load balancing processes considered in an initial network entry, network reentry and handover are controlled through a ranging process, but they must consider the following difference. In the case of an initial network entry, because there is no information about a service flow in a ranging process, only the user number is checked. In the case of a network reentry/handover, because not only the user number but also information about a service flow can be checked in a ranging process, it is necessary to additionally consider the service flow number and the bandwidth (BW) of each service flow as well as the user number. In view of service continuity, because a service does not start in an initial access and re-access, it is preferable to induce a reentry in an initial network entry or network reentry for load balancing. Also, it is preferable to induce a handover in load balancing for a seamless service because a service is being provided in a handover.
Fourth, there may be a case where the subscriber number limit is not exceeded in the network reentry/handover and there is no candidate subcell that can allow all the service flows of the corresponding user terminal. What is therefore required is a scheme for providing against the case where some service flows are allowed but the remaining service flows are not allowed.